Time base corrector

Abstract

Whenever component signals (color difference signals) of a video tape recorder signal are recorded in a recording medium in accordance with timeplex (time division multiplex) method, velocity error inevitably occurs because there always exists a difference in relative velocity between a tape head and tape between recording process and reproducing process. To eliminate the velocity errors included in the component signals when reading out the signals, a first read clock signal is generated to read a first component signal recorded in the first half of each horizontal period segment under consideration of integral velocity error as in the conventional method, and a second read clock signal is generated to read a second component signal recorded in the second half of each horizontal period segment under consideration of both initial offset velocity error and integral velocity error.

What is claimed is: 
     
       1. A time base corrector for correcting time base fluctuations in a reproduced video signal VI recorded on a recording medium in such a format that at least two timeplexed video component signals R-Y and B-Y are recorded in one horizontal period segment 1H, which includes: a clock generator for generating a write clock signal CL having time base fluctuations included in the reproduced video signal;   a memory unit for storing the reproduced video signal VI in response to the write clock signal CL;   a velocity error detector for detecting velocity error included in the reproduced video signal and outputting a velocity error signal RER corresponding thereto; and   a read clock generator including a velocity error compensator for generating read clock signals RCK phase-modulated in dependence upon the velocity error signal RER to read the stored reproduced video signal from said memory unit while correcting the time base fluctuations and velocity error, characterized in that said velocity error compensator comprises:   means for generating a first integral velocity error signal V1 for a first timeplexed video component signal signal RY in response to the velocity error signal RER;   means for generating a second integral velocity error signal V3 including an initial offset value V2 relative to the first integral velocity error signal V1 for a second timeplexed video component signal B-Y in response to the velocity error signal RER; and   means for phase-modulating a reference clock signal having a frequency substantially the same as that of the write clock signal CL with the first and second integral velocity error signals V1 and V3 to generate at least two read clock signals RCKR and RCKB for sequentially and separately reading the at least two timeplexed video component signals.   
     
     
       2. The time base corrector as set forth in claim 1, wherein said first integral velocity error signal generating means is an integrator of opeational amplifier type including a capacitor. 
     
     
       3. The time base corrector as set forth in claim 1, wherein said second integral velocity error signal generating means comprises an initial phase error generator for generating said initial offset value V2 relative to the first integral velocity error signal V1 and an adder for adding the first integral velocity error signal V1 and the initial offset value V2 relative to the first integral velocity error signal. 
     
     
       4. The time base corrector as set forth in claim 1, wherein said phase modulating means comprises at least two comparators for comparing the first and second integral velocity error signals V1 and V3 with a sawtooth signal STH generated in response to the reference clock signal to generate said at least two pulse width modulated read clock signals RCKR and RCKB. 
     
     
       5. A time base corrector for correcting time base fluctuations in a reproduced video signal VI recorded on a recording medium in such a format that at least two timeplexed video component signals R-Y and B-Y are recorded in one horizontal period segment 1H, which comprises: memory means;   means for generating a write clock signal CL on the basis of a horizontal synchronizing signal HSY and a burst signal BST extracted from a reproduced video signal VI and which is employed to sequentially write in said memory means picture element data included in the timeplexed video component signals recorded on the recording medium;   means for detecting an error voltage signal SER corresponding to a phase difference generated in the write clock signal CL within each horizontal period segment;   means for temporarily storing the generated error voltage signal SER; and   means for generating a first read clock signal RCKR pulse width modulated on the basis of a sawtooth wave signal STH and a first integral velocity error signal V1 obtained by integrating the error voltage signal SER, and simultaneously a second read clock signal RCKB pulse width modulated on the basis of the sawtooth wave signal STH and an addition signal V3 of the first integral velocity error signal V1 and an error signal V2 corresponding to a phase difference detected at a record-start point t 01  of the second timeplexed video component signal B-Y, said first and second read clock signals being applied to said memory means in order to sequentially read therefrom said picture element data written in the memory means.   
     
     
       6. The time base corrector as set forth in claim, 5 wherein said means for generating said first and second read clock signals comprises: an integrator for integrating the error voltage signal SER stored in said error voltage signal storing means to obtain the first integral velocity error signal V1;   an initial phase error generator for generating the error signal V2 corresponding to an initial phase difference detected at a record-start point t 01  of the second timeplexed video component signal B-Y;   an adder for adding the first integral velocity error signal V1 and the error signal V2 to obtain a second integral velocity error signal V3;   a sawtooth generator for generating the sawtooth signal STH in response to a reference signal;   a first comparator for comparing the first integral velocity error signal V1 with the sawtooth signal STH to generate the first pulse width modulated read clock signal RCKR when the first error signal V1 exceeds the sawtooth signal STH in voltage level; and   a second comparator for comparing the second integral velocity error signal V3 with the sawtooth signal STH to generate the second pulse width modulated read clock signal RCKB when the second error signal V3 exceeds the sawtooth signal STH in voltage level.   
     
     
       7. A method of correcting time base fluctuations in a reproduced video signal VI recorded on a recording medium in such a format that at least two timeplexed video component signals R-Y and B-Y are in one horizontal period segment 1H, which comprises the steps of: extracting a horizontal synchronizing signal HSY and a burst signal BST from the reproduced video signal;   generating a write clock signal CL in response to the horizontal synchronizing signal HSY and the burst signal BST;   sequentially writing in a memory in response to said write clock signal CL picture element data included in the timeplexed video component signals reproduced from the recording medium;   detecting a phase difference generated in the write clock signal CL within each horizontal period segment and outputting an error voltage signal SER corresponding thereto;   temporarily storing the error voltage signal SER and outputting a stored velocity error signal RER at appropriate timings;   integrating the velocity error signal RER and outputting a first integral velocity error signal V1 corresponding thereto;   detecting an initial phase difference at a recordstart point t 01  of the second timeplexed video component signal B-Y and outputting an error signal V2 corresponding thereto;   adding the first integral velocity error signal V1 and the error signal V2 and outputting a second integral velocity error signal V3;   generating a sawtooth wave signal STH in response to a reference signal REF;   pulse width modulating the sawtooth wave signal STH with the first integral velocity signal V1 to generate a first read clock signal RCKR operative to sequentially read from said memory the picture element data in the first timeplexed component signal R-Y of the video signal reproduced from the recording medium; and   pulse width modulating the sawtooth wave signal STH with the second integral velocity signal V3 to generate a second read clock signal RCKB operative to sequentially read from said memory the picture element data in the second timeplexed component signal B-Y of the video signal reproduced from the recording medium.